This invention relates to testing and characterization of microwave high power transistors and amplifiers (device under test, DUT); the test system disclosed here allows for high volume, high speed production testing chips on wafer through acquisition and processing of its RF characteristics, typically gain, output power, efficiency, inter-modulation etc, under precise source and load impedance at the fundamental and harmonic frequencies (see ref. 1); reflection factors Γ up to and exceeding |Γ|=1. The complex RF impedance Z=R+jX relates to the complex reflection factor Γ as follows: Γ=|Γ|*exp(jΦ)=(Z−Zo)/(Z+Zo), whereby Zo=50Ω is the typical characteristic impedance of the transmission lines, cables and input/output instrument impedances in the system.